<div style="width: calc(100% - 20px);height: 30px;padding: 10px;background-color: rgb(228, 228, 228);">
    <button onclick="window.location.href='./qq_1.html'"><</button>
    私聊</div>
<div class="a_3" id="chat_content_4" style="overflow-y: scroll;width: calc(100%-10px);padding: 5px;background-color: white;height: 70vh;">

</div>
<style>
    .a_3 button {
        width: 100%;
        padding: 5px;
        background-color: aliceblue;
        margin-top: 3px;
        text-align: left;
    }
</style>